Adjustable coupling system



June 26, 1951 A. e. MANKE 2,558,573

ADJUSTABLE COUPLING SYSTEM Filed 001;. 12, 1949 SEC. FRI. SEC.

Ihventor Arthur G. M'anKe His Attorney Patented June 26, 1951 ADJUSTABLE COUPLING SYSTEM Arthur G. Manke, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application October 12, 1949, Serial No. 121,027

2 Claims; (01. 171-119) This invention relates to electrical coupling ap paratus, and particularly to means for adjusting the self inductance of inductively-coupled windings without changing the mutual inductance therebetween.

In the manufacture of radio apparatus, it is generally necessary that circuits be aligned or tuned to the operating frequency, after the apparatus has been assembled. This is necessitated by reason of unavoidable manufacturing tolerances, and requires that circuits having adjustable components be provided.

In the construction of radio frequency coils, it is frequently desirable to have a coil construction such that final adjustment of the secondary winding inductance can be made by means of a movable magnetic core. It is then important that the mutual inductance between the primary and secondary windings remains substantially constant when the core which adjusts the secondary inductance is moved, and it is also desirable that this core be effective in reducing the required number of turns on the primary winding. This is usually accomplished by arranging the coils so that the core enters the magnetic fields of both windings in such a way that movement of the core, within certain limits, does not affect the primary inductance.

My invention is particularly concerned with a transformer construction wherein two secondary windings are mounted on one form, and a single primary winding is used to provide inductive coupling. It is an object of my invention to pro-' vide a core arrangement, in conjunction with such a coil structure, which permits separate adjustments of both secondary inductances without causing any substantial change in the mutual inductance between the primary and each of the secondary windings.

A further object of my invention is to provide a new and more economical core arrangement for a multiple-coil high-frequency, coupling transformer than has been available heretofore, and which permits a reduced number of turns on a primary winding.

For further objects and advantages and for a better understanding of my invention, attention is now directed to the following description and accompanying drawing. The features of my invention believed to be novel will be more particularly pointed out in the appended claims.

The single figure of the drawing is a crosssectional view of a three-winding transformer structure and core arrangement embodying my invention.

Referring to the drawing, the transformer comprises a primary winding and a pair of secondary windings, mounted coaxially on a cylindrical dielectric form I. The primary winding is provided by a coil 2 which is mounted approximately at the center of form I. A single coil 3 provides the first secondary winding and is mounted to the right of primary coil 2 and at a short distance therefrom to provide a desired value of mutual inductance. The second secondary winding is provided by two pie sections 4 and 5, which are mounted at a short distance to the left of the primary winding, both sections being also separated one from each other by an axial gap.

It is desired that the self inductances of both secondary windings be separately adjustable and that substantially no change occur in the mutual inductances of the secondaries with respect to the primary winding as a result of their individual adjustments. In accordance with my invention, this feature is provided by means of two cylindrical magnetic cores, 6 and l, disposed as shown in the drawing. These cores may be any one of a number of types commonly utilized in high frequency circuits. For instance, they may be composed of carbonyl iron powder in a resin binder, the whole having been compressed to a suitable cylindrical shape as shown. Both cores are provided with adjustin rods or screws 8 and 9, respectively, threaded into suitable supports (not shown). The cores 8 and 9 are thus mounted within the form I so that they may be displaced axially with respect to the windings. Core 6 is provided with an insulating end por tion 10 into which the adjusting rod 8 is fitted, whereas core I has its adjusting rod 9 mounted directly into the magnetic material.

These cores permit an adjustment of the inductance of the windings because they provide a magnetic path of lower reluctance than air for the magnetic field surrounding the coil. Axial displacement of each core causes a change in the inductance of a winding inasmuch as one edge of the core is located in a region of high magnetic density. A very small movement of the core therefore produces a sizable change in the flux distribution, and, accordingly, in the inductance of the winding affected thereby. Thus, the right edge of core 6 is located approximately in the center of secondary winding 3 and any axial displacement of core 6 will provide a relatively large change in the self inductance of 3. However, as for the mutual inductance between coils 2 and 3, the axial displacement of core 6 affects the flux distribution between coils 2 and moans 8 relatively little, and therefore, causes very little change in the mutual inductance.

Similarly, the left-hand edge of core 6 is situated approximately in the center of the gap between the two sections 4 and of the second secondary winding. This edge, therefore, moves in a region of relatively low flux density and does not cause any substantial change in the flux distribution and in the self inductance of the second secondary winding 45. Displacement of core 6 hardly affects the magnetic fiux existing between the primary winding and the second secondary winding. This follows from the fact that the larger part of the fiux providing the mutual inductance exists between coils 2 and 5, and axial displacement of core 6 does not affect the flux distribution in this region. It is to be understood, naturally, in this discussion of the effect of any movement of cor 6, that the movement is restricted to a narrow range bounded approximately by the center and the right-hand edge of winding 3.

Core 1 is provided for the purpose of permitting an adjustment in the self inductance of the second secondary winding. Since the right-hand edge of core I is located approximately at the center of section 4, it can be seen that this edge is located in a region of relatively high flux density. Accordingly, when the core is moved, a relatively large change is produced in the flux distribution through section 4, thereby producing a relatively rapid rate of change in the selfhductance of the second secondary winding with respect to axial displacement of this core.

My invention thus provides a transformer and core structure in which the self inductances of two secondary windings may be adjusted practically independently of each other and of the mutual coupling to a common primary winding. It will be understood that the left edge of core 6 may provide some change in the self inductance of the second secondary winding, inasmuch as it may move in a region which contains some of the magnetic flux linking pie sections 4 and 5. The

extent of the change caused thereby may be reduced by providing a greater separation between the two pies. On the other hand, where too large a separation is undesirable, any slight change in the self inductance of the second secondary winding produced by movement of core 6 may be corrected by moving core I. In a practical radio circuit, it is generally possible to provide for the adjustment of the windings in a definite sequence. inductance of secondary winding 3 by means of core 6 it is then possible to adjust the second secondary winding 4-5 by means of core I, without reference to any slight increment in inductance which may have been caused originally by axial displacement of core 6.

It will be observed that the transformer and core arrangement which I have described permits a reduction in the number of turns of wire in the primary winding over conventional structures, since magnetic core 6 is inserted through its center. Moreover my structure has the advantage that only two magnetic 60185 are required for the whole transformer structure rather than requiring a separate core for the primary and Thus by first adjusting the self each of the secondary windings. This again is a considerable advantage which permits an eco- While a certain specific embodiment has been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. For example, it is entirely possible to provide all of the windings as multiple section coils. The appended claims are, therefore, intended to cover any such modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical coupling system comprising three coaxially mounted, inductively-coupled windings spaced along an axis, an outer one of said windings being constructed of two pie sections with a predetermined axial gap therebetween, a pair of magnetic cores of uniform crosssection adjustably mounted for axial movement within said windings, one of said cores having a length substantially equal to the distance from the mid point of the gap between said pies to the center point of the other outer winding, said one core being normally located between said points, the other of said cores being normally located so that it penetrates to the center of the outer pie of said one outer winding from the opposite side of said gap. l

2. A high-frequency coupling transformer comprising a primary winding and a pair of secondary windings coaxially mounted on either side of said primary winding, said secondary windings being axially spaced from said primary winding, one of said secondary windings being composed of two pie sections with an axial gap therebetween, a pair of magnetic cores of uniform cross-section mounted for axial movement withinsaid windings, one of said cores having a length such that, in its normal mounting position, it extends from the center of said gap to the center of said other secondary winding, and the other of said cores being disposed such that, in its normal mounting position, it penetrates to the center of the outer one of said pies from the opposite side of said gap, whereby axial displacement of said cores provides adjustment of the self inductances of said secondary windings with substantially no effect on the mutual inductance between each of said secondary windings and said primary winding.

ARTHUR G. MANKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,582,497 Waters Apr. 27, 1926 2,441,116 Mackey May 4, 1948 2,507,344 Macgeorge May 9, 1950 

